WRc is using ‘state-of-the-art’ technology and techniques to measure bubble size and bubble size distributions in wastewater treatment aeration systems. The bubble size measurement technique is being tested to see if it can potentially provide a more accurate means of determining aeration efficiency. The technique offers an opportunity to identify whether a plant is performing to design specification and to identify diffuser maintenance/replacement needs. The research is being undertaken as part of the ongoing Portfolio collaborative project ‘CP489 Advanced Aeration Efficiency’.
Until now, correlations for the performance of diffused aeration systems have included the effect of bubble size but, in the absence of bubble size measurements, have relied upon the use of additional correlations to estimate the diameter.
Direct measurement permits the calculation of the bubble size and the frequency of bubbles of that size, from which the Sauter mean diameter (the diameter that will calculate the correct surface area for mass transfer) can be calculated. Typically, diffused aeration bubble sizes are in the range of 2 – 5 mm.
For one of the sites monitored, the correlations predicted a bubble size of 4.9 mm, and a gas voidage of 0.24%, compared to the direct measurement producing a bubble size of 3.5 mm and a gas voidage of 0.86%. The smaller bubble size means that the diffused air system is around 30% more efficient than would have been estimated without the use of direct measurements. On-site trials will continue in 2014.
For further information contact Kevin Poole on 01793 865179 or firstname.lastname@example.org.